Referring to FIG. 1, a conventional storage box 1 includes a hollow box body 11, and first and second covers 12, 13 for removably covering the hollow box body 11. The second cover 13 is connected to and rotatory relative to the first cover 12 so that the storage box 1 is openable to for accessing articles in the hollow box body 11. Additionally, the second cover 13 has an edge formed with a plurality of long grooves 131 for rotatory engagement of the first cover 12 therewith. However, a gap is formed between the first cover 12 and the second cover 13. Water may permeate the hollow box body 11 through the gap when the storage box 1 comes accidentally in contact with the water, and thus, the protection effect of the conventional storage box 1 needs improvement.